Compared to conventional half duplex communication in which time or frequency resources are divided orthogonally, full duplex communication doubles a system capacity in theory by allowing a node to perform transmission and reception simultaneously.
FIG. 1 is a conceptual view of a user equipment (UE) and a base station (BS) which support full duplex radio (FUR).
In the FDR situation illustrated in FIG. 1, the following three types of interference are produced.
Intra-apparatus self-interference: Because transmission and reception take place in the same time and frequency resources, a desired signal and a signal transmitted from a BS or UE are received at the same time at the BS or UE. The transmitted signal is received with almost no attenuation at a reception (Rx) antenna of the BS or UE, and thus with much larger power than the desired signal. As a result, the transmitted signal serves as interference.
UE to UE inter-link interference: An uplink (UL) signal transmitted by a UE is received at an adjacent UE and thus serves as interference.
BS to BS inter-link interference: The BS to BS inter-link interference refers to interference caused by signals that are transmitted between BSs or heterogeneous BSs (pico, femto, and relay) in a HetNet state and received by an Rx antenna of another BS.
Among such three types of interference, intra-apparatus self-interference (hereinafter, self-interference (SI)) is generated only in an FDR system to significantly deteriorate performance of the FDR system. Therefore, first of all, intra-apparatus SI needs to be cancelled in order to operate the FDR system.